Project Summary: The long-term goals of this project focus on establishing the ATP-binding cassette transporter-2 (ABCA2) as a novel regulator of proteolytic processing of the amyloid precursor protein (APR). Amyloidogenic processing of APP results in the generation of A-beta peptide cleavage products that are implicated in the etiology of Alzheimer's disease (AD). The complete elucidation of the mechanisms that regulate APP processing and Ap production has not been realized. One mechanism that regulates APP processing is the cholesterol trafficking-dependent localization of APP and key enzymes that mediate its proteolytic cleavage in membrane compartments. ABCA2 may function to modulate intracellular cholesterol trafficking of exogenous llpoprotein-derived cholesterol from late-endosomes/lysosomes to membrane compartments. We identified ABCA2 as a regulator of APP processing and A-beta production in vitro. We determined that cellular APP holoprotein levels and A-beta secretion were increased in non-neuronal HEK293 cells that stably co-expressed ABCA2 and APP bearing the APP "Swedish" mutation. We also detected increased expression of a number of genes associated with AD using microarray analysis in HEK293 cells that stably expressed ABCA2. Although evidence suggests that ABCA2 may be a key regulator of APP metabolism, perhaps by regulation of intracellular cholesterol trafficking and distribution, we have not examined the effects of ABCA2 function in either neuronal cells or in the brains of transgenic mice expressing mutant forms of APP. Our recent production of ABCA2 knockout mice and ABCA2 transgenic mice under the control of the brain-specific Thy-1 promoter will permit the investigation of this novel function of the ABCA2 transporter in regulating APP processing and A-beta production in vivo in transgenic mouse models of AD. Our preliminary results have led us to the novel hypothesis that ABCA2 acts to regulate APP processing and A-beta production through modulation of intracellular cholesterol trafficking-dependent localization of APP and key processing enzymes in membrane compartments. Public Health Relevance: These studies may provide novel and mechanistic links between cholesterol metabolism and APP processing that could be of direct clinical relevance. In depth knowledge of the mechanisms of action of the ABCA2 transporter on regulation of APP processing may provide a basis for the development of therapeutic strategies in prevention and treatment of AD.